Data storage device

ABSTRACT

The present disclosure relates to a data storage device. The data storage device comprises a closed interior space containing a noble gas, a plurality of electron emitters having emission surfaces exposed within the interior space, the electron emitters adapted to emit electron beams, and a storage medium contained within the interior space in proximity to the electron emitters, the storage medium having a plurality of storage areas that are capable of at least two distinct states that represent data, the state of the storage areas being changeable in response to bombardment by electron beams emitted by the electron emitters.

FIELD OF THE INVENTION

The present disclosure relates to a data storage device. Moreparticularly, the disclosure relates to a data storage device includinga mechanism for removing contaminants from emission surfaces of electronemitters within the device.

BACKGROUND OF THE INVENTION

Researchers have continually attempted to increase the storage densityand reduce the cost of data storage devices such as magnetichard-drives, optical drives, and dynamic random access memory (DRAM).Recently, semiconductor-based electron sources have been developed thatcan be used in storage devices and which may avoid the difficultiesnoted above. An example of such a data storage device is described inU.S. Pat. No. 5,557,596. The device described in that patent includesmultiple electron emitters having electron emission surfaces that face astorage medium. During write operations, the electron sources bombardthe storage medium with relatively high intensity electron beams. Duringread operations, the electron sources bombard the storage medium withrelatively low intensity electron beams. Such a device providesadvantageous results. For instance, the size of storage bits in suchdevices may be reduced by decreasing the electron beam diameter, therebyincreasing storage density and capacity and decreasing storage cost.

During fabrication, various contaminants from the ambient air can formon the electron emission surfaces of the data storage device. Suchcontaminants include various materials containing oxygen, nitrogen,and/or carbon. Perhaps most problematic of these is carbonaceousmaterials such as hydrocarbons. The formation of contaminants isdisadvantageous in that their presence adversely affects operation ofthe electron emitters. For instance, the presence of contaminantsincreases electron scattering. In addition, where the electron emitterscomprise field (i.e., tip) emitters, the work function of the emitterscan be decreased, lowering the potential needed to emit electron beamsfrom the emitters and thereby raising the currents substantially. Thisphenomenon makes it more difficult to control operation of the emittersin that the magnitude of the electron beams emitted from the emittersmay be greater than desired, therefore increasing the opportunity formisreading and/or miswriting to a storage medium of the device. Removingthese contaminants from the atmosphere to prevent their deposition onthe electron emission surfaces during fabrication is difficult, if notimpossible.

In addition to contaminants present in the ambient air duringfabrication, further contaminants can be deposited on the emissionsurfaces of the electron emitters. For example, if the storage medium ofthe device is partially decomposed, or if contaminants on the surfaceare desorbed, during read and/or write operations, volatile componentscan be released that will settle on the electron emission surfaces. Likethe airborne contaminants referenced above, these contaminants cansimilarly result in electron scattering and may significantly changeemitter operational characteristics.

From the foregoing, it can be appreciated that it would be desirable tohave a data storage device that employs a mechanism to removecontaminants from the emission surfaces of the electron emitterscontained within the device.

SUMMARY OF THE INVENTION

The present disclosure relates to a data storage device. The datastorage device comprises a closed interior space containing a noble gas,a plurality of electron emitters having emission surfaces exposed withinthe interior space, the electron emitters adapted to emit electronbeams, and a storage medium contained within the interior space inproximity to the electron emitters, the storage medium having aplurality of storage areas that are capable of at least two distinctstates that represent data, the state of the storage areas beingchangeable in response to bombardment by electron beams emitted by theelectron emitters.

In addition, the present disclosure relates to a method for removingcontaminants from an electron emission surface of an electron emitter ofa data storage device. The method comprises the steps of providing anoble gas within an interior space of the data storage device to whichthe electron emission surface is exposed, exciting atoms within the gasby impacting them with an electron beam emitted by the electron emitter,wherein the atoms of the gas are ionized by impact with the electronbeam and accelerated toward the emission surface to sputter remove thecontaminants from the emission surface.

In preferred arrangements, the noble gas used in the device and methodcomprises neon gas.

The features and advantages of the invention will become apparent uponreading the following specification, when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be better understood with reference to the followingdrawings. The components in the drawings are not necessarily to scale,emphasis instead being placed upon clearly illustrating the principlesof the present invention.

FIG. 1 is a schematic side view of an example data storage device.

FIG. 2 is a schematic cross-sectional view of the data storage device ofFIG. 1 taken along line 2—2.

FIG. 3 is a schematic cross-sectional perspective view of the datastorage device of FIGS. 1 and 2 taken along line 3—3.

FIG. 4 is a partial schematic view of a storage medium of the datastorage device shown in FIGS. 1-3.

FIG. 5 is a schematic side view of a first example reading arrangementfor the data storage device of FIGS. 1-4.

FIG. 6 is a schematic side view of a second example reading arrangementfor the data storage device of FIGS. 1-4.

DETAILED DESCRIPTION

Referring now in more detail to the drawings, in which like numeralsindicate corresponding parts throughout the several views, FIGS. 1-3illustrate an example data storage device 100. It is noted that thisdevice 100 is similar in construction to that described in U.S. Pat. No.5,557,596, which is hereby incorporated by reference into the presentdisclosure.

As indicated in FIGS. 1-3 the data storage device 100 generally includesan outer casing 102 that forms an interior space 104 therein. By way ofexample, the casing 102 can include a plurality of walls 106 that definethe interior space 104. Typically, the walls 106 of the casing 102 aresealed to each other such that a vacuum can be maintained within theinterior space 104. By way of example, the casing 102 maintains a vacuumof at least approximately 10⁻³ Torr within the interior space 104. As isdescribed in greater detail below, the interior space preferablycontains a noble gas, such as neon gas, which removes contaminants fromemission surfaces within the device 100. Although a particularconfiguration is shown for the casing 102, it is to be understood thatthe casing can take many different forms that would be readily apparentto persons having ordinary skill in the art.

Within the interior space 104 is a plurality of electron emitters 108that face a storage medium 110. These electron emitters can, forexample, comprise field (i.e., tip) emitters as described in U.S. Pat.No. 5,557,596 identified above. Alternatively, the electron emitters 108can comprise flat emitters such as those described in U.S. patentapplication Ser. No. 09/836,124, filed Apr. 16, 2001, which is herebyincorporated by reference into the present disclosure. As described inrelation to FIG. 4, the storage medium 110 comprises a plurality ofstorage areas (not visible in FIGS. 1-3). In a preferred embodiment,each storage area of the storage medium 110 is responsible for storingone or bits more of data. The electron emitters 108 are configured toemit electron beam currents toward the storage areas of the storagemedium 110 when a predetermined potential difference is applied to theelectron emitters. Depending upon the distance between the emitters 108and the storage medium 110, the type of emitters, and the spot size(i.e., bit size) required, electron optics may be useful in focusing theelectron beams. Voltage is also applied to the storage medium 110 toaccelerate the emitted electrons to aid in focusing the emittedelectrons.

Each electron emitter 108 can serve many different storage areas towrite data to and read data from the storage medium 110. To facilitatealignment between each electron emitter 108 and an associated storagearea, the electron emitters and storage medium can be moved relative toeach other in the X and Y directions noted in FIG. 2. To provide forthis relative movement, the data storage device 100 can include amicromover 112 that scans the storage medium 110 with respect to theelectron emitters 108. As indicated in FIGS. 1 and 3, the micromover 112can include a rotor 114 connected to the storage medium 110, a stator116 that faces the rotor, and one or more springs 118 that arepositioned to the sides of the storage medium. As is known in the art,displacement of the rotor 114, and thereby the storage medium 110, canbe effected by the application of appropriate potentials to electrodes117 of the stator 116 so as to create a field that displaces the rotor114 in a desired manner.

When the micromover 112 is displaced in this manner, the micromoverscans the storage medium 110 to different locations within the X-Y planesuch that each emitter 108 is positioned above a particular storagearea. A preferred micromover 112 preferably has sufficient range andresolution to position the storage areas 110 under the electron emitters108 with high accuracy. By way of example, the micromover 112 can befabricated through semiconductor microfabrication processes. Althoughrelative movement between the electron emitters 108 and the storagemedium 110 has been described as being accomplished through displacementof the storage medium, it will be understood that such relative movementcan alternatively be obtained by displacing the electron emitters or bydisplacing both the electron emitters and the storage medium. Moreover,although a particular micromover 112 is shown and described herein, itwill be appreciated by persons having ordinary skill in the art thatalternative moving means could be employed to obtain such relativemovement.

Alignment of an emitted beam and storage area can be further facilitatedwith deflectors (not shown). By way of example, the electron beams canbe rastered over the surface of the storage medium 110 by eitherelectrostatically or electromagnetically deflecting them, as through useof electrostatic and/or electromagnetic deflectors positioned adjacentthe emitters 108. Many different approaches to deflect electron beamscan be found in literature on scanning electron microscopy (SEM).

The electron emitters 108 are responsible for reading and writinginformation on the storage areas of the storage medium with the electronbeams they produce. Therefore, the electron emitters 108 preferablyproduce electron beams that are narrow enough to achieve the desired bitdensity for the storage medium 110, and that provide the different powerdensities needed for reading from and writing to the medium. Particularexample embodiments for the electron emitters 108 are provided later inthis disclosure.

As indicated in FIGS. 1 and 2, the data storage device 100 can furtherinclude one or more supports 120 that support the storage medium 110 inplace within the interior space 104. When provided, the supports 120typically comprise thin-walled microfabricated beams that flex when thestorage medium 110 is displaced in the X and/or Y directions. As isfurther indicated in FIGS. 1 and 2, the supports 120 can each beconnected to the walls 106 of the casing 102 or alternatively to thestator 116.

In a preferred embodiment, the electron emitters 108 are containedwithin a two-dimensional array comprising a plurality of emitters. Byway of example, an array of 100×100 electron emitters 108 can beprovided with an emitter pitch of approximately 5 to 100 micrometers inboth the X and Y directions. As discussed above, each emitter 108typically is used to access a plurality of storage areas of the storagemedium 110. FIG. 4 provides a schematic representation of thisrelationship. In particular, this figure illustrates a single electronemitter 108 positioned above a plurality of storage areas 400 of thestorage medium 110. As indicated in FIG. 4, the storage areas 400, likethe electron emitters 108, are contained in a two-dimensional array. Inparticular, the storage areas 400 are arranged in separate rows 402 andcolumns 404 on the surface of the storage medium 110. In a preferred anembodiment, each emitter 108 is only responsible for a portion of theentire length of predetermined numbers of rows 402. Accordingly, eachemitter 108 normally can access a matrix of storage areas 400 ofparticular rows 402 and columns 404. Preferably, each row 402 that isaccessed by a single electron emitter 108 is connected to a singleexternal circuit.

To address a storage area 400, the micromover 112 is activated todisplace the storage medium 110 (and/or electron emitters 108) to alignthe storage area with a particular electron emitter. Typically, eachemitter 108 can access tens of thousands to hundreds of millions ofstorage areas 400 in this manner. The storage medium 110 can have aperiodicity of approximately 5 to 100 nanometers between any two storageareas 400, and the range of the micromover 112 can be approximately 15micrometers. As will be appreciated by persons having ordinary skill inthe art, each of the electron emitters 108 can be addressedsimultaneously or in a multiplexed manner. A parallel accessing schemecan be used to significantly increase the data rate of the storagedevice 100.

Writing with the data storage device 100 is accomplished by temporarilyincreasing the power density of an electron beam produced by an electronemitter 108 to modify the surface state of a storage area 400 of thestorage medium 110. For instance, the modified state can represent a “1”bit, while the unmodified state can represent a “0” bit. Moreover, thestorage areas can be modified to different degrees to represent morethan two bits, if desired. In a preferred embodiment, the storage medium110 is constructed of a material whose structural state can be changedfrom crystalline to amorphous by electron beams. An example material isgermanium telluride (GeTe) and ternary alloys based on GeTe. To changefrom the amorphous to the crystalline state, the beam power density canbe increased and then slowly decreased. This increase/decrease heats theamorphous area and then slowly cools it so that the area has time toanneal into its crystalline state. To change from the crystalline toamorphous state, the beam power density is increased to a high level andthen rapidly reduced. Although temporary modification of the storagemedium 110 is described herein, it will be understood that permanentmodification is possible where write-once-read-many (WORM) functionalityis desired.

Reading is accomplished by observing the effect of the electron beam onthe storage area 400, or the effect of the storage area on the electronbeam. During reading, the power density of the electron beam is kept lowenough so that no further writing occurs. In a first reading approach,reading is accomplished by collecting the secondary and/or backscatteredelectrons when an electron beam with a relatively low (ie., lower thanthat needed to write) power density is applied to the storage medium110. In that the amorphous state has a different secondary electronemission coefficient (SEEC) and backscattered electron coefficient (BEC)than the crystalline state, a different number of secondary andbackscattered electrons are emitted from a storage area 400 whenbombarded with a read electron beam. By measuring the number ofsecondary and backscattered electrons, the state of the storage area 106can be determined.

FIG. 5 illustrates example apparatus for reading according to the firstreading approach. More particularly, FIG. 5 schematically illustrateselectron emitters 108 reading from storage areas 500 and 502 of thestorage medium 110. In this figure, the state of storage area 500 hasbeen modified, while the state of storage area 502 has not. When a beam504 of electrons bombard the storage areas 500, 502 both the secondaryelectrons and backscattered electrons are collected by electroncollectors 506. As will be appreciated by persons having ordinary skillin the art, modified storage area 500 will produce a different number ofsecondary electrons and backscattered electrons as compared tounmodified storage area 502. The number may be greater or lesserdepending upon the type of material and the type of modification made.By monitoring the magnitude of the signal current collected by theelectron collectors 506, the state of and, in turn, the bit stored inthe storage areas 500 and 502 can be identified.

In another reading approach, a diode structure is used to determine thestate of the storage areas 400. According to this approach, the storagemedium 110 is configured as a diode which can, for example, comprise ap-n junction, a schottky, barrier, or substantially any other type ofelectronic valve. FIG. 6 illustrates an example configuration of such astorage medium 110. It will be understood that alternative diodearrangements (such as those shown in U.S. Pat. No. 5,557,596) arefeasible. As indicated in this figure, the storage medium 110 isarranged as a diode having two layers 600 and 602. By way of example,one of the layers is p type and the other is n type. The storage medium110 is connected to an external circuit 604 that reverse-biases thestorage medium. With this arrangement, bits are stored by locallymodifying the storage medium 110 in such a way that collectionefficiency for minority carriers generated by a modified region 608 isdifferent from that of an unmodified region 606. The collectionefficiency for minority carriers can be defined as the fraction ofminority carriers generated by the instant electrons that are sweptacross a diode junction 610 of the storage medium 110 when the medium isbiased by the external circuit 604 to cause a signal current 612 to flowthrough the external circuit.

In use, the electron emitters 108 emit narrow beams 614 of electronsonto the surface of the storage medium 110 that excite electron-holepairs near the surface of the medium. Because the medium 110 isreverse-biased by the external circuit 604, the minority carriers thatare generated by the incident electrons are swept toward the diodejunction 610. Electrons that reach the junction 610 are then sweptacross the junction. Accordingly, minority carriers that do notrecombine with majority carriers before reaching the junction 610 areswept across the junction, causing a current flow in the externalcircuit 604.

As described above, writing is accomplished by increasing the powerdensity of electron beams enough to locally alter the physicalproperties of the storage medium 110. Where the medium 110 is configuredas that shown in FIG. 6, this alteration affects the number of minoritycarriers swept across the junction 610 when the same area is radiatedwith a lower power density read electron beam. For instance, therecombination rate in a written (i.e., modified) area 608 could beincreased relative to an unwritten (i.e., unmodified) area 606 so thatthe minority carriers generated in the written area have an increasedprobability of recombining with minority carriers before they have achance to reach and cross the junction 610. Hence, a smaller currentflows in the external circuit 604 when the read electron beam isincident upon a written area 608 than when it is incident upon anunwritten area 606. Conversely, it is also possible to start with adiode structure having a high recombination rate and to write bits bylocally reducing the recombination rate. The magnitude of the currentresulting from the minority carriers depends upon the state ofparticular storage area, and the current continues the output signal 612to indicate the bit stored.

As identified above, various contaminants can form on the electronemission surfaces of the electron emitters 108 during fabrication of thedata storage device 100 and/or thereafter. The interior space 104 of thedata storage device 100 therefore preferably contains a noble gas thatremoves the contaminants from the emitter emission surfaces during useof the emitters. In a preferred arrangement, this noble gas comprisesneon gas. Neon gas is preferable because it is massive enough to removethe contaminants, yet not so massive as to damage the electron emitters108.

The mechanism with which the selected gas removes the contaminants fromthe electron emitters pertains to ionization of the gas during datastorage device use. Specifically, when an electron beam is emitted froman electron emitter 108, the beam impacts atoms of the gas, exiting themto the point at which the atoms lose an electron and therefore ionize.Due to their positive charge, the generated ions are attracted to thenegative charge of the electron emitters 108, and are accelerated towardthe electron emitters such that they ultimately bombard the emissionsurfaces of the electron emitters. In that the ions have a mass similarto that of the contaminants residing on the emission surface, thecontaminants are displaced (i.e., sputter removed) from the surface bythe ions, thereby cleaning the emission surfaces and ensuring properoperation of the electron emitters 108.

The strength of the vacuum maintained within the interior space maydepend upon the type of electron emitters 108 used in the fabrication ofthe data storage device 100. Due to the use of the gas within theinterior space 104, the vacuum need not be as strong as when air remainswithin the space. By way of example, where field emitters are used, thevacuum preferably is approximately 10⁻⁴ to 10⁻⁶ Torr, with 10⁻³ Torrpossible. For flat emitters, the vacuum preferably is approximately 10⁻³to 10⁻⁶ Torr. In any case, however, the strength of the vacuum ismaintained such that plasma generation within the interior space 104 isavoided.

While particular embodiments of the invention have been disclosed indetail in the foregoing description and drawings for purposes ofexample, it will be understood by those skilled in the art thatvariations and modifications thereof can be made without departing fromthe scope of the invention as set forth in the following claims.

What is claimed is:
 1. A data storage device, comprising: a sealed outercasing that forms an interior space; a noble gas provided within theinterior space; a plurality of electron emitters having emissionsurfaces exposed within the interior space, the electron emittersadapted to emit electron beams; and a storage medium contained withinthe interior space in proximity to the electron emitters, the storagemedium having a plurality of storage areas that are capable of at leasttwo distinct states that represent data, the state of the storage areasbeing changeable in response to bombardment by electron beams emitted bythe electron emitters, wherein the noble gas provided within theinterior space removes contaminants from the emission surfaces of theelectron emitters during at least one of data storage and dataretrieval;
 2. The device of claim 1, wherein the interior space ismaintained in a vacuum.
 3. The device of claim 2, wherein the vacuum isless than approximately 10⁻⁶ Torr.
 4. The device of claim 3, wherein thevacuum is greater than approximately 10⁻³ Torr.
 5. The device of claim1, wherein the electron emitter comprises a field emitter.
 6. The deviceof claim 1, wherein the electron emitter comprises a flat emitter. 7.The device of claim 1, wherein the noble gas is neon gas.
 8. A datastorage device, comprising: a sealed outer casing that defines a sealedinterior space; a plurality of electron emitters having emissionsurfaces exposed within the sealed interior space, the electron emittersadapted to emit electron beams; a storage medium contained within theinterior space in proximity to the electron emitters, the storage mediumhaving a plurality of storage areas that are capable of at least twodistinct states that represent data, the state of the storage areasbeing changeable in response to bombardment by electron beams emitted bythe electron emitters; and a noble gas provided within the sealedinterior space for removing contaminants from the emission surface ofthe electron emitter during at least one of the data storage and dataretrieval.
 9. The device of claim 8, wherein the interior space ismaintained in a vacuum.
 10. The device of claim 9, wherein the vacuum isless than approximately 10⁻⁶ Torr.
 11. The device of claim 9, whereinthe vacuum is greater than approximately 10⁻³ Torr.
 12. The device ofclaim 8, wherein the electron emitter comprises a field emitter.
 13. Thedevice of claim 8, wherein the electron emitter comprises a flatemitter.
 14. The device of claim 8, wherein the noble gas is neon gas.15. A method comprising: forming a data storage device including aninterior space; providing a noble gas within the interior space; andsealing the interior noble gas such that the space is maintained in avacuum within the interior space; and removing contaminants fromemission surfaces of electron emitters within the interior space withthe noble gas during at least one of data storage and data retrievalusing the electron emitters.
 16. The method of claim 15, wherein theelectron emitters are adapted to emit electron beams and the datastorage device includes a storage area that is capable of at least twodistinct states that represent data.
 17. The method of claim 15, furthercomprising ionizing the neon gas during one of data storage and dataretrieval.
 18. The method of claim 15, further comprising bombarding anemission surface of an electron emitter within the interior space withnoble gas ions.
 19. The method of claim 15, further comprising sputterremoving contaminants from an emission surface of an electron emitterwithin the interior space.
 20. The method of claim 15, furthercomprising storing data to the data storage device while the interiorspace is maintained in the vacuum with the noble gas provided therein.21. The method of claim 15, further comprising reading data from thedata storage device while the interior space is maintained in the vacuumwith the noble gas provided therein.
 22. The method of claim 15, whereinthe noble gas is neon gas.
 23. A method for removing contaminants froman emission surface of an electron emitter of a data storage device,comprising: providing a noble gas within an interior space of the datastorage device to which the emission surface is exposed; exciting atomswithin the gas by impacting them with an electron beam emitted by theelectron emitter during at least one of the data storage and dataretrieval; wherein the atoms of the noble gas are ionized by impact withthe electron beam and accelerated toward the emission surface to sputterremove the contaminants from the emission surface.
 24. The method ofclaim 23, further comprising sealing the interior space with the neongas contained therein.
 25. The method of claim 23, wherein the noble gasis neon gas.